Bottom Line:
Using species distribution models, climatic analyses, spatial connectivity and morphological comparisons, we found significant differences in climatic and morphological variables between populations of N. parviflora in two distinct Trans-Mexican Volcanic Belt regions (east vs. west).Spatial connectivity analysis revealed no connectivity between these regions under the present or last glacial maximum climate models, indicating a lack of gene flow between the populations of the two regions.The results imply that these populations may encompass more than a single species.

ABSTRACTThe hypothesis of ecological speciation states that as populations diverge in different niches, reproductive isolation evolves as a by-product of adaptation to these different environments. In this context, we used Nolina parviflora as a model to test if this species evolved via ecological speciation and to explore current and historical gene flow among its populations. Nolina parviflora is a montane species endemic to Mexico with its geographical distribution restricted largely to the Trans-Mexican Volcanic Belt. This mountain range is one of the most complex geological regions in Mexico, having undergone volcanism from the mid-Miocene to the present. Ecologically, the Trans-Mexican Volcanic Belt possesses different types of vegetation, including tropical dry forest; oak, pine, pine-oak, and pine-juniper forests; and xerophytic scrub--all of which maintain populations of N. parviflora. Using species distribution models, climatic analyses, spatial connectivity and morphological comparisons, we found significant differences in climatic and morphological variables between populations of N. parviflora in two distinct Trans-Mexican Volcanic Belt regions (east vs. west). This could mean that the geographically isolated populations diverged from one another via niche divergence, indicating ecological speciation. Spatial connectivity analysis revealed no connectivity between these regions under the present or last glacial maximum climate models, indicating a lack of gene flow between the populations of the two regions. The results imply that these populations may encompass more than a single species.

Mentions:
The statistical parsimony network recovered 11 different haplotypes among N. parviflora populations. The most frequent haplotype (H6) is shared by populations from Puebla, Tlaxcala and Veracruz, and represents 44.3% of all individuals sampled. This haplotype is geographically distributed in the easternmost part of the TMVB. The second most frequent haplotype (H1) is shared by populations in the states of Edo. México, Hidalgo and Michoacán, and represents 32.2% of all individuals sampled. H1 is geographically distributed in the eastern region of the TMVB. Haplotypes H2 and H3 are shared between the Jalisco and Zacatecas populations in the western region of the TMVB. Haplotypes H4 and H5 are unique to the MICH and MEX1 populations, respectively. Haplotype H7 is shared by the PUE2, 4, 9 and VER populations; and finally haplotypes H8 and H11 are unique to the PUE4 and ZAC populations (Table 1, Fig. 2). Haplotypes H2–3, H9–11 are exclusive to the western part of the TMVB and are not shared with any populations occurring in the eastern area of the TMVB. Haplotypes H1, H4 and H5 are distributed in the eastern region of the TMVB and are not shared with any of the easternmost populations. Finally H6, H7 and H8 are only found in the easternmost part of the TMVB (Fig. 2).

Mentions:
The statistical parsimony network recovered 11 different haplotypes among N. parviflora populations. The most frequent haplotype (H6) is shared by populations from Puebla, Tlaxcala and Veracruz, and represents 44.3% of all individuals sampled. This haplotype is geographically distributed in the easternmost part of the TMVB. The second most frequent haplotype (H1) is shared by populations in the states of Edo. México, Hidalgo and Michoacán, and represents 32.2% of all individuals sampled. H1 is geographically distributed in the eastern region of the TMVB. Haplotypes H2 and H3 are shared between the Jalisco and Zacatecas populations in the western region of the TMVB. Haplotypes H4 and H5 are unique to the MICH and MEX1 populations, respectively. Haplotype H7 is shared by the PUE2, 4, 9 and VER populations; and finally haplotypes H8 and H11 are unique to the PUE4 and ZAC populations (Table 1, Fig. 2). Haplotypes H2–3, H9–11 are exclusive to the western part of the TMVB and are not shared with any populations occurring in the eastern area of the TMVB. Haplotypes H1, H4 and H5 are distributed in the eastern region of the TMVB and are not shared with any of the easternmost populations. Finally H6, H7 and H8 are only found in the easternmost part of the TMVB (Fig. 2).

Bottom Line:
Using species distribution models, climatic analyses, spatial connectivity and morphological comparisons, we found significant differences in climatic and morphological variables between populations of N. parviflora in two distinct Trans-Mexican Volcanic Belt regions (east vs. west).Spatial connectivity analysis revealed no connectivity between these regions under the present or last glacial maximum climate models, indicating a lack of gene flow between the populations of the two regions.The results imply that these populations may encompass more than a single species.

ABSTRACTThe hypothesis of ecological speciation states that as populations diverge in different niches, reproductive isolation evolves as a by-product of adaptation to these different environments. In this context, we used Nolina parviflora as a model to test if this species evolved via ecological speciation and to explore current and historical gene flow among its populations. Nolina parviflora is a montane species endemic to Mexico with its geographical distribution restricted largely to the Trans-Mexican Volcanic Belt. This mountain range is one of the most complex geological regions in Mexico, having undergone volcanism from the mid-Miocene to the present. Ecologically, the Trans-Mexican Volcanic Belt possesses different types of vegetation, including tropical dry forest; oak, pine, pine-oak, and pine-juniper forests; and xerophytic scrub--all of which maintain populations of N. parviflora. Using species distribution models, climatic analyses, spatial connectivity and morphological comparisons, we found significant differences in climatic and morphological variables between populations of N. parviflora in two distinct Trans-Mexican Volcanic Belt regions (east vs. west). This could mean that the geographically isolated populations diverged from one another via niche divergence, indicating ecological speciation. Spatial connectivity analysis revealed no connectivity between these regions under the present or last glacial maximum climate models, indicating a lack of gene flow between the populations of the two regions. The results imply that these populations may encompass more than a single species.